US5313310A - Tonal conversion method for pictures - Google Patents

Tonal conversion method for pictures Download PDF

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US5313310A
US5313310A US07/481,054 US48105490A US5313310A US 5313310 A US5313310 A US 5313310A US 48105490 A US48105490 A US 48105490A US 5313310 A US5313310 A US 5313310A
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picture
density
original
tonal conversion
color
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Takashi Numakura
Iwao Numakura
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Yamatoya and Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/407—Control or modification of tonal gradation or of extreme levels, e.g. background level
    • H04N1/4072—Control or modification of tonal gradation or of extreme levels, e.g. background level dependent on the contents of the original

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  • This invention relates to a tonal conversion method of picture, which is indispensable upon producing various types of reproduced pictures including hard pictures such as printed pictures, and reproduced digital pictures, and soft pictures (transient images displayed optically) such as CRT (video) pictures from original pictures (which will hereinafter be equally called “medium pictures”) stored and recorded on various recording media such as photographic photosensitive materials, photoelectric materials, and photoconductive materials.
  • this invention relates to an improved tonal conversion method in which an attention is paid to physical quantities correlating densities of a camera subject (real picture or actual scene) which is a basis of an original picture (medium picture) such as light exposures incident from the camera subject in the case of a photographic picture, said physical quantities relating to light quantities incident from a camera subject being going to be hereinafter called "pictorial information values".
  • a conventional tonal conversion technique in which an attention is paid to values of an original picture (medium picture) recorded on a recording medium or physical quantities correlating to density values such as current or voltage values stored on a photoelectric material such as CCD.
  • the term "pictures” as used herein should be interpreted in a broad sense so that it embraces not only pictures themselves but also images.
  • the present invention relates to a novel tonal conversion method in which the picture information obtained from a camera subject (real picture, actual scene), which should be a direct object for a reproduced picture, is considered more important than the picture information obtained from an original picture (medium picture), which is put a stress thereon in the conventional method.
  • the tonal conversion method of this invention relates not only to a method for a reproduced picture having a tone faithful to its original picture therefrom but also to a method for adjusting (correcting or modifying) the tone of the reproduced picture as desired.
  • Reproduced pictures such as printed pictures, reproduced pictures, printer pictures, television (Video) pictures, etc. are produced from original pictures of continuous tone by various types of reproduction techniques, as known well.
  • the term "reproduced pictures” should be interpreted in a broadest sense as described above.
  • it is extremely important to faithfully reproduce the gradation and tone of an original picture on its reproduced picture in a systematic manner. It is however the present state of art that no basic technique has yet been established to permit conversion of an original picture into a reproduced picture rationally and effectively in a systematic manner, in spite of advancement of the techniques for producing reproduced pictures in recent years.
  • the conventional technique has no idea to rationally grasp the density characteristic of an original picture in the range of from highlight to shadow areas upon producing a printed color picture as a reproduced picture from a color film original. Approximately 90% of color original pictures are transparent type. Further, the conventional technique is totally dependent upon the experiences and perception of an operator upon determining a correlation of picture characteristics between an original picture and a printed reproduced picture, or upon setting color-separation characteristic curves (equally called "color-separation characteristic curves" or "halftone characteristic curves”), which determine a correlation between an original picture of continuous tone and a printed reproduced picture in halftone.
  • the original color picture Upon producing a printed color picture in halftone from an original color picture, the original color picture is subjected to color separation by a color scanner to make color plates (C, M, Y and K, in general).
  • the problem is that which size of a halftone dot should be corresponded to a given picture element of an original color picture.
  • machines and systems for color separation have been developed, although a basic technique for designing machines and systems is still in an immature level.
  • the practical work heavily depends on the experiences and perception of an operator, while using such expensive and highly advanced electronic color-separation system. From the above reasons, constant supply of printed color pictures having stable qualities is difficult in the present state. Specifically, there exists a serious problem in the case that a color original has been produced under in appropriate conditions such as photographing, exposing and developing conditions, or a color original has color-fog thereon.
  • the conventional techniques fail to provide rational color separation work to cope with such the color originals of non-standard picture qualities. Furthermore, there exist another problems in the conventional techniques such as a low operation rate of scanners, unstable quality of a reproduced picture, increase of rescanning work, etc. as previously mentioned.
  • the present inventors have a view that in order to establish a rational theory in the tonal conversion technique of pictures and produce rationally reproduced pictures having reproducibility of tone (gradation and tone) and further reproduced pictures having desired tone from various types of originals, a respect should be given to a technique capable of providing rational density conversion of each picture element of a picture, prior to giving an attention to an improvement of the color correction technique.
  • the density gradation of elements is reproduced on a reproduced picture by varying the size of the halftone dots or the like, by changing the arrangement of the defined dots, or by changing the density of the picture elements themselves.
  • an emphasis is laid on the color correction which is comparatively easy to be analyzed in a scientific manner in the conventional technique rather than the tonal conversion in the density range.
  • the present inventors have a view that in the conventional tonal conversion technique of pictures in the density range used upon producing a reproduced picture from an original color picture, a density characteristic of the original picture, for example a color film original picture for producing a printed color picture as a reproduced picture, in the range of from the highlight to shadow areas thereof is not rationally grasped, besides no rational theory has yet been established to determine a correlation (a tonal conversion formula) between two pictures (i.e., an original picture and a reproduced picture), which is indispensable upon faithfully converting the density characteristic of the original picture at the ratio of 1:1 into the reproduced picture. Therefore, the conventional technique is totally dependent upon the experiences and perception of man in this point.
  • the limitation is that in the conventional technique including proposals by the present inventors, the tonal conversion of pictures is conducted on the basis of information values relating to density information of an original picture (medium picture) stored or recorded on a recording medium (i.e., a photosensitive material, a photoelectric material, a photoconductive material, etc.), instead of pictorial information values of a camera subject (real picture, actual scene), which should be considered as a direct object for a reproduced picture.
  • a recording medium i.e., a photosensitive material, a photoelectric material, a photoconductive material, etc.
  • a photographic density is formed by development on a photosensitive material of a film on which a camera subject has been photographed, said photographic density forming an original picture (medium picture), as well known.
  • a curve showing a correlation between the photographic densities (blackening degrees) and the light exposures E of a photographic photosensitive material is a photographic characteristic curve.
  • a ratio of an intensity of transparent light I to an intensity of incident light I o is used for films or dry plates and a ratio of an intensity of reflected light I to an intensity of perfect reflected light I o for photographic printing paper (reflection original).
  • a typical photographic characteristic curve (hereinafter called "a density characteristic curve”) has a considerably complex shape, which has a downwardly-curved leg portion, an approximately linear middle portion, and an upwardly-curved shoulder portion (see FIGS. 1 and 4).
  • the shape of the density characteristic curve is determined dependent upon the characteristics of a photosensitive material of a film, namely, the type of a photosensitive material developed by the manufacturer.
  • the present color separation technique is built up on the basis of the axis of ordinates (density values) of the density characteristic curve.
  • the picture information of an original color picture which is considered to form the basis of color separation in the conventional technique, is not in a relationship proportional to picture information of a camera subject (real picture, actual scene) and the degree of estrangement between them are dependent upon the exposure condition, developing condition, etc.
  • the photographic densities which are picture information values of an original color picture (medium picture) cannot be correlated in a linear relation (for example, at 45° at the ratio of 1:1, if plotted on a coordinate system) to the picture information values (for example, physical quantities such as exposure quantities or the like) relating to the light quantities incident from a camera subject.
  • the discrimination characteristics of human visual sensation to light and shade is logarithmic and man evaluates a camera subject (real picture, actual scene) on the basis of said discrimination characteristics.
  • the human visual sensation empirically evaluates it natural what has a density change with a linear gradient.
  • An object of the invention is to provide a novel technique for producing a reproduced picture from an original picture, in which a weight is laid on picture information obtained from a camera subject (real picture, actual scene), said camera subject being a direct object for the reproduced picture, instead of picture information of an original picture (medium picture), which is laid a weight thereon in the conventional technique, and specifically to provide a novel tonal conversion technique of pictures which is the core of said technique.
  • the present invention relates to a method for conducting a tonal conversion of a picture upon production of a reproduced picture from an original picture as a medium picture recorded on a given recording medium from a camera subject as a real picture, which comprises the steps of:
  • y a tone intensity value of the picture element on the reproduced picture corresponding to the desired picture element on the original picture
  • y H a tone intensity value set for the brightest area (H) on the original picture or on the corresponding area of the camera subject;
  • y S a tone intensity value such as a dot area percentage set for the darkest area (S) on the original picture or on the corresponding area of the camera subject;
  • ⁇ a surface reflectance of a base material used for expressing the reproduced picture thereon
  • X Sn represents the pictorial information value (X Sn ) of the camera subject determined by the density value (D Sn ) of the darkest area (S) on the original picture in accordance with the density characteristic curve;
  • ⁇ a desired optional factor.
  • FIG. 1 is a diagrammatic illustration of a density characteristic curve of a color film
  • FIG. 2 is a diagrammatic illustration of color separation curves of the X axis plotted on the basis of the density characteristic curve of FIG. 1, in accordance with the present invention
  • FIG. 3 is a diagrammatic illustration of color separation curves of the D axis plotted on the basis of the density characteristic curve of FIG. 1, in accordance with a conventional technique;
  • FIG. 4 is a diagrammatic illustration of a density characteristic curve which is voluntarily plotted
  • FIG. 5 is a diagrammatic illustration of color separation curves of the X axis plotted on the basis of the density characteristic curve of FIG. 4, in accordance with the present invention.
  • FIG. 6 is a diagrammatic illustration of color separation curves of the D axis plotted on the basis of the density characteristic curve of FIG. 4, in accordance with the conventional technique.
  • the tonal conversion method useful upon producing a reproduced picture from an original picture (medium picture) in accordance with the present invention will be described by way of production of a printed color picture (medium picture) as a reproduced picture. It should be noted that the tonal conversion method of pictures in accordance with the present invention is not limited only to the case of production of a printed color picture, this description being only for convenience.
  • a color scanner system for color-separation is widely used upon production of a printed color pictures these days.
  • Color-separation performed by a color scanner is based on density information values (including transparent and reflection originals) obtained from an original color picture (medium picture).
  • density information values including transparent and reflection originals
  • M magenta
  • Y yellow
  • BK black
  • R red
  • G green
  • B blue
  • the conventional technique has a limitation (disadvantage) that the density information values of an original color picture (medium picture) recorded on a recording medium such as a photographic photosensitive material are utilized therein, as previously mentioned.
  • the present invention is, on the contrary, based on a view that an direct object for a reproduced picture should be a camera subject (real picture, actual scene) itself, not a picture recorded on a recording medium, hence picture information values directly obtained from the camera subject should be used.
  • Density values of an original picture of continuous gradation should be converted into halftone dot area percentage on a reproduced picture. It is a color separation curve to define a correlation between a picture of continuous gradation and a halftone picture.
  • the conventional color separation curve is determined on the basis of density values on the D axis of an original picture (medium picture). On the contrary, the color separation curve is determined on the basis of picture information values on the X axis of a camera subject (real picture, actual scene) in the present invention, as mentioned above.
  • a color separation curve of the X axis (refer FIGS. 2 and 5) is adopted in the resent invention.
  • the so-determined density characteristic curve is then represented by functional formulae to obtain X n value (D n ⁇ X n ) in the next step. It is adequate to represent various types of photographic characteristic curves provided by the photosensitive material manufacturer by functional formulae, for instance. So long as the density characteristic curve is rationally represented by functional formulae, the D n value on the D axis may be readily converted into the X n value on the X axis.
  • Density characteristic curves used in Examples of this invention are shown in FIGS. 1 and 4.
  • One shown in FIG. 4 was voluntarily determined by the present inventors for inspecting the generality and reliability of the tonal conversion method of pictures in accordance with this invention.
  • a density characteristic curve may be formulated as follows:
  • leg portion of the density characteristic curve i.e., downwardly curved portion, an area having small D values
  • shoulder portion i.e., upwardly curved portion, an area having large D values
  • FIGS. 1 and 4 Details of the formulated density characteristic curves depicted in FIGS. 1 and 4 are shown in TABLE 1, where a plurality of sections are provided for formulating the density characteristic curves as accurate as possible.
  • the D and X values were represented by functional formulae, assuming that X axis showing the picture information values expressed in log E of a camera subject (real picture), said X axis having a scale graduated identical to that of the D axis showing the density values of an original color picture (medium picture), as shown in FIGS. 1 and 4. It should be noted that the X axis shown in FIGS. 1, 2, 4 and 5 is assigned to indicate picture densities of a camera subject (fictitious values).
  • the present invention is, as previously described, based on picture information values provided by a camera subject (real picture, actual scene), i.e., physical quantities (X n values) relating to the light quantities represented on the X axis, not on density information values (D n ) of an original picture (medium picture).
  • the picture information values provided by the camera subject may be obtained. Strictly speaking, they are deformed by a lens system or the like more or less, but it can be ignored.
  • the thus-determined X n values and the tonal conversion formula derived from this invention are used to determine a color separation curve of the X axis instead of a conventional color separation curve of the D axis, and it is only necessary to conduct tonal conversion of the picture thereafter.
  • the picture information value (X n ) of a desired picture element on the camera subject is determined from the density value (D n ) of the corresponding picture element on the original picture (medium picture) through a predetermined density characteristic curve and said X n value is substituted in the tonal conversion formula, whereby a dot area percentage which is a gradational intensity value is calculated.
  • the dot area percent value thus-obtained is inputted to a halftone dot generator of a color scanner to form a desired reproduced picture on the screen.
  • ⁇ the surface reflectance of the printing ink.
  • the tonal conversion formula of this invention was derived on the basis of the above density formula (D') relating to plate-making and printing in a manner that a X n value on the X axis is determined from a density value (D n ) on the D axis of a desired sample point (picture element) on the original picture of continuous gradation, a basic density value (x) is determined therefrom, and a theoretical formula which is used for determining a dot area percentage (y) of a halftone dot on a printed picture in halftone corresponding to said basic density value (x) is established.
  • the tonal conversion formula of this invention is so established that a theoretical value calculated from said theoretical formula is agreed with an actual measured value.
  • cyan (C), magenta (M), yellow (Y), and black (BK) plates are generally considered to make up a unit, the cyan plate (C) being served as a basic plate.
  • Parameters of y H and y S are generally dealt as constants. For instance, 5% and 95% of dot area percent values are adopted as y H and y S for the C plate respectively, and 3% and 90% of dot area percent values are adopted as y H and y S for the M and Y plates, respectively.
  • y value is computed as a percent value.
  • Numerical values set to the parameters in the tonal conversion formula are varied dependent on a purpose, that is, when the tone of a given camera subject (real picture) is desired to be faithfully reproduced on a printed picture, or when the tone of a printed picture is desired to be voluntarily adjusted (corrected or modified).
  • One of the features of the tonal conversion formula derived from this invention is that the shape of a color separation curve of the X axis may be voluntarily changed by varying the ⁇ value therein.
  • the shape of the color separation curve of the X axis is changed as desired by varying the ⁇ value, whereby a printed pictures of one of various tones is obtained.
  • the reason why such the numerical value is adopted as the ⁇ value is that the yellow ink has the largest excitation value to the visual sensation of man among the printing inks besides this conforms to the practical work of color separation. It is needless to say that another value may be adopted as the ⁇ value upon setting a color separation curve of the X axis, in this sense.
  • a manner for setting color separation curves of the X axis for the respective color plates, C, M, Y and B plates being considered to make up a unit, by conducting the tonal conversion formula of this invention in multicolor plate-making process is as follows.
  • the tonal conversion formula is conducted from a standpoint of view that a color separation curve for the C plate, which is considered to be the most important plate among the four color plates, is rationally determined. Accordingly, a color separation curve of the X axis for the C plate is primarily determined by conducting the tonal conversion formula.
  • Color separation curves of the X axis for the other M and Y plates are secondary determined by multiplying an appropriate regulating value well known in the art so as to maintain the gray and color balance on a picture.
  • a color separation curve of the X axis for the black (BK) plate may be determined according to the practical manner in the field of art from a view point such as reduction of consumed quantities of C, M and Y inks, etc.
  • each of the color separation curve for the respective color plates may be determined as follows. Namely, a color separation curve of the X axis for the C plate is determined through the density characteristic curve of the corresponding emulsion layer of R to begin with, color separation curves of the X axis for the M and Y plates are subsequently determined through the respective density characteristic curves of G and B so as to maintain the color and (gray) balance on a reproduced picture. In this case, it is needless to say that appropriate ⁇ values should be adopted for the respective M and Y plates in the tonal conversion formula.
  • the present invention permits to provide a printed color pictures having a picture image faithful to a camera subject (real picture, actual scene) with generality and flexibility in a systematic manner, on the assumption that density values (D n ) of an original color picture (medium picture) are not used therein, but picture information values (X n ) of the camera subject (substantial picture) are used therein upon conducting the tonal conversion formula derived from this invention.
  • the tonal conversion technique of pictures according to this present invention is applied not only to production of color printed pictures as previously mentioned, but to various kinds of application fields as hereinafter described. Namely, it can be applied to all fields where picture information values obtained by photographing or photograph-converting the picture information of a real picture are processed to obtain output information of a reproduced picture, utilizing information transmitting media such as light, electromagnetic wave, or the like.
  • the tonal conversion technique of pictures should be, of course, suitably conducted so as to be adapted to a given system used for producing reproduced pictures.
  • the tonal conversion method of this invention is primarily not limited to only a combination of density values and logarithmic values of light exposure upon setting a density characteristic curve showing a correlation between information values relating to the density information of an original picture (medium picture) and pictorial information values of a camera subject (real picture, actual scene).
  • Any picture information of a camera subject inputted by means of a sensor of a system for producing a reproduced picture is adoptable so long as it correlates to the density information values.
  • Physical quantity correlating to information values relating to density information of a camera subject (real picture) inputted by means of a sensor to a recording medium or the like should be interpreted in a broadest sense.
  • Synonyms may include reflected density, transmitted density, luminance, lightness, light quantity, amplitude, current and voltage values, etc. Any one of a photographic photosensitive material, a photoelectric material, a photoconductive material, an optical disk, a magnetic disk (recording medium), etc. may be employed as a recording medium for recording an original picture (medium picture).
  • the surface reflectance, for example, of a printing paper (base material) to be used to express or visualizing the picture to be printed is set at 100%.
  • ⁇ any desired value may be chosen. From the practical viewpoint, it may be set at 1.0. This also applies to luminance pictures such as video pictures.
  • y H and y S can be set respectively for the highlight area H and the shadow area S on the printed picture as intended, which constitutes one of remarkable features of this invention.
  • the tonal conversion technique of pictures using the tonal conversion formula derived in this invention therein is extremely useful for reproducing the gradation and color tone of a camera subject, namely, for reproducing the tone of a camera subject at the ratio of 1:1 on a printed picture in a systematic manner. It should be noted that its usefulness is not limited only to such an application. In addition to its reproducibility with fidelity to the characteristics of a camera subject, the tonal conversion formula is also extremely useful for rational modification or correction of the picture characteristics by suitably selecting the values ⁇ , ⁇ , ⁇ , y H , and y S therein.
  • the tonal conversion method of this invention can also be applied effectively to the following cases.
  • the tonal conversion method of this invention can be applied to densitometers equipped with a density and tone conversion system to display a tone area percent and the like along with a density, printing-related equipment such as simulators for advance testing of color separation (for example, color proofing simulators) and simulators for the education of color separation, etc.
  • a system for making an original printing plate by exposing an original picture (medium picture), which is a continuous-tone picture such as a color photograph, to a spot light of a small diameter, receiving at a photoelectric conversion unit (photomultiplier) light (a pictorial information signal) reflected by or transmitted through the original picture, processing the thus-obtained electrical signal (electrical value) of pictorial information by a computer as needed, controlling an exposing light source based on a processed electrical signal (voltage) of pictorial information outputted from the computer, and then exposing a blank film to a laser spot light.
  • an original picture medium picture
  • photoelectric conversion unit photomultiplier
  • Such a software may take any one of various forms such as a general purpose computer storing an algorithm of the tonal conversion formula derived in this invention as a software and having an I/F (interface) for AD (analogdigital conversion) and D/A, an electric circuit embodying the algorithm as a logic by a general purpose IC, an electric circuit with a ROM containing results computed in accordance with the algorithm, a PAL, gate array or custom IC with the algorithm embodied as an internal logic, etc.
  • a general purpose computer storing an algorithm of the tonal conversion formula derived in this invention as a software and having an I/F (interface) for AD (analogdigital conversion) and D/A, an electric circuit embodying the algorithm as a logic by a general purpose IC, an electric circuit with a ROM containing results computed in accordance with the algorithm, a PAL, gate array or custom IC with the algorithm embodied as an internal logic, etc.
  • a computing system capable of performing tonal conversion of a picture in its density range on the basis of the tonal conversion formula derived in this invention can be easily fabricated as a module of a special-purpose IC, LSI, microprocesor, microcomputer or the like.
  • An original printing plate of a halftone gradation having the dot area percent (value y) derived by the tonal conversion formula can be easily made by causing a photoelectrically-scanning spot light to advance successively as discrete spots and operating a laser exposing unit in unison with the scanning.
  • the tonal conversion method of this invention brings about the following advantages:
  • the conventional color separation technique of which core is a technique for setting color separation curves of the D axis, starts primarily from an original picture (medium picture) recorded on a recording medium which is a photographic photosensitive material (emulsion).
  • a recording medium which is a photographic photosensitive material (emulsion).
  • the color separation technique according to this invention of which core is a technique for setting color separation curves of the X axis, there is adopted a manner directly approaching a camera subject (real picture, actual scene) itself but a picture image of the camera subject recorded on a recording medium.
  • This invention therefore permits to provided printed color pictures more faithful to a camera subject (real picture, actual scene).
  • the conventional technique which is a technique for setting a color separation curve of D axis, provides a different color separation curve for a given color original so that the most suitable color separation curve should be determined for the given color original on each occasion.
  • the color separation method of this invention permits to provide a single color separation curve irrespective of the picture quality of the original picture, or irrespective of the density range determined on the density characteristic curve (the curve including a straight line) of the original picture and the shape of the density characteristic curve (including a straight line), so long as same numerical values are set at the ⁇ , y H , y S and ⁇ values respectively in the tonal conversion formula, thereby uniformly representing the tone of a printed color pictures obtained after being subjected to color-separation.
  • tone (arrangement of dot area % values) of a printed color picture to be reproduced may be rationally and objectively judged from the shape of a color separation curve of the X axis in advance. Namely, it is possible that the tone of a printed color picture may be confirmed or adjusted in advance by reading out the tone of a printed color picture from the shape of the color separation curve of the X axis and the arrangement of the dot area percent values. This makes it possible to omit printer's proof (hard or soft proof) exclusive of orders's proof. Change or modification of the tone of an original picture may be rationally coped with by adjusting the parameters (especially ⁇ value) in the tonal conversion formula derived in this invention.
  • the tonal conversion technique of this invention allows to provide a color separation curve of the X axis which gives an appropriate picture quality to a printed picture, even in the case that a plurality of the density characteristic curves of photographic photosensitive materials of color originals are not represented by a same density characteristic area, an original picture has nonstandard (under- or over-exposed) picture quality, to say nothing of standard quality, or an original picture has color-fog thereon.
  • the tonal conversion method of this invention can automatically absorb or process these usual and unusual elements and simultaneously and automatically solve the problems relating to color-fog and color-balance (gray-balance), thereby making it possible to provide a printed color pictures with excellent picture quality.
  • a condition for conducting the tonal conversion formula is as follows:
  • TABLES 2(A1) to 2(A3) show over-exposed original pictures, i.e., original pictures in light tone
  • TABLES 2(B1) to 2(B4) show original pictures substantially appropriately-exposed
  • TABLES 2(C1) to 2(C3) show original pictures under-exposed, i.e., original pictures in dark tone.
  • FIG. 2 shows color separation curves of the X axis (relation between X n ' and y, as previously described) in accordance with the present invention.
  • FIG. 3 shows color separation curves of the D axis, which shows a relation between D n ' and y.
  • the color separation curves shown in FIG. 3 is regarded as an example for setting color separation curves in accordance with the conventional technique.
  • the conventional technique provides a plurality of color separation curves each corresponding to the respective color originals, as shown in FIG. 3. It is therefore impossible to learn in advance the resulting tone of a printed picture after color separation.
  • FIGS. 5 and 6 Color separation curves plotted on the bases of the data shown in from TABLE 3(A1) to TABLE 3(C3) are depicted in FIGS. 5 and 6. Plotting of the color separation curves was carried out in a manner quite similar to Example 1. Astonishing facts is also found from FIGS. 5 (the present invention) and 6 (the conventional technique) as same in Example 1. As superposing FIG. 5 on FIG. 2, it is found that their color separation curves are quite identical. It means that even if the premised density characteristic curves are different, an identical color separation curve of the X axis is obtained so long as the y H , y S and ⁇ values each takes respective same values upon conducting the tonal conversion formula derived in this invention.
  • the tonal conversion technique of pictures of this invention may be effectively applied, even in the case that density characteristic curves of photographic photosensitive materials of a plurality of color originals are not represented by an identical density characteristic curve, the color originals have thick color-fog thereon, or the density characteristic curves are in relation transversely parallel to each other or each of the density characteristic curves has a different gradient due to color-fog.
  • a color separation curve of the D axis of a linear density characteristic curve is plotted in FIG. 6 [Refer (L) in FIG. 6]. It is obtained from a straight line drawn as a diagonal at 45° in a X-D coordinate system. Another examples in which color separation curves are obtained from a linear density characteristic curve utilizing the density characteristic curve shown in FIG. 1 will next be inspected.
  • a density characteristic curve having a linear shape was made utilizing the density characteristic curve depicted in FIG. 1 as follows:
  • a curve obtained by plotting the data of TABLE 5 comes out to be completely identical to the color separation curve of the X axis shown in FIG. 2, as similar to the aforementioned.
  • the tonal conversion method of this invention allows to provide an identical color separation curves of the X axis when the y H , y S , and ⁇ values in the tonal conversion formula each takes the same value respectively, even if the density characteristic straight lines (not curves) are different with each other.
  • original pictures to be subjected to color separation by a color scanner are classified into two types in general, i.e., reflection originals such as watercolor paintings, oil paintings, etc. and transparent original such as positive and negative film pictures.
  • the reflection originals have density characteristic curves having an approximately linear shapes, of which real pictures themselves are subjected to be color separation.
  • the real pictures are so evaluated by visual sensation of man in the light of logarithmic optical density that the real pictures have linear density gradients.
  • transparent originals are negative or positive photographic films of which photosensitive materials have density characteristic curves (photographic characteristic curves) having curved shapes. It is evident that the tonal conversion method of this invention is effective to refection originals having linear density characteristic curves.
  • the tonal conversion method of this invention is also applicable to various types of original pictures, irrespective whether the originals are of refection type or transparent type.
  • Color printed pictures were produced from the following color originals (1) and (2) in size 4" ⁇ 5".
  • color originals each having a different density values in the range of from the highlight area (H) to the shadow area (S) shown in TABLE 6 are prepared.
  • a condition of the parameters in the tonal conversion formula for setting a color separation curve of the X axis for the C plate is as follows:
  • the same color separation curve was used for both the M and Y plates.
  • a color separation curve of the X axis for BK plate was determined in accordance with the ordinary practical manner.
  • Color separation was performed by employing Magnascan M-645 (tradename, manufactured by Crosfield Electronics Limited) as a color scanner. Relating to color proofing, color-proofing printed pictures were produced by a Chromarine proof press (manufactured by Du Pont), then evaluation was made on picture qualities of the resulting proofing pictures.
  • the color-proofing printed pictures for the respective three originals thus-produced had the picture qualities in a substantially same tone, as expected. Every one of them is well expressed or visualized in its highlight and shadow parts and has a density gradient in the range of from the highlight to shadow parts, which is felt natural to visual sensation of man.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Facsimile Image Signal Circuits (AREA)
  • Image Processing (AREA)
  • Color Electrophotography (AREA)
  • Facsimiles In General (AREA)
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JP1-135825 1989-05-31
JP1135825A JP2939270B2 (ja) 1989-05-31 1989-05-31 画像の階調変換法

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5913014A (en) * 1997-07-21 1999-06-15 Eastman Kodak Company Transforms for digital images
US6433898B1 (en) * 1995-08-26 2002-08-13 Heidelberger Druckmaschinen Aktiengesellschaft Method and apparatus for the conversion of color values
US6842266B1 (en) * 2000-02-25 2005-01-11 Xerox Corporation Systems and methods that determine an image processing system tone reproduction curve
US20060034323A1 (en) * 2004-08-11 2006-02-16 Lars Karlsson Method and technique for the processing and intelligent display of wideband direction-finding data
US20070287395A1 (en) * 2004-08-11 2007-12-13 Lars Karlsson Method and signal intelligence collection system that reduces output data overflow in real-time

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JP2787231B2 (ja) * 1989-08-19 1998-08-13 株式会社ヤマトヤ商会 色カブリのない複製画像を製作するための画像の階調変換法
JPH03258164A (ja) * 1990-03-08 1991-11-18 Yamatoya & Co Ltd 画像形成装置
JP2873329B2 (ja) * 1990-11-09 1999-03-24 株式会社ヤマトヤ商会 画像の階調変換法
JP3129755B2 (ja) * 1991-02-04 2001-01-31 株式会社ヤマトヤ商会 多色製版用墨版カーブの設定法
JP2955071B2 (ja) * 1991-07-30 1999-10-04 株式会社ヤマトヤ商会 退色カラー写真原稿の階調変換法
JPH0750761A (ja) * 1993-08-06 1995-02-21 Yamatoya & Co Ltd 独立タイプの入・出力機で構成される画像処理システムの色再現法
JP2007006530A (ja) * 2006-09-08 2007-01-11 Toppan Printing Co Ltd 墨版量および分解４原色量の決定方法と、それらを利用した原色変換方法と装置

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US4833546A (en) * 1987-03-11 1989-05-23 Yamatoya & Co., Ltd. Photomechanical apparatus
US4924323A (en) * 1988-05-13 1990-05-08 Yamatoya & Co., Ltd. Tonal conversion method for pictures
US4956718A (en) * 1988-08-23 1990-09-11 Yamatoya & Co., Ltd. Tonal conversion method for pictures
US5057931A (en) * 1989-08-19 1991-10-15 Yamatoya & Co., Ltd. Tonal conversion method of pictures for producing reproduced pictures free of color-fog
US5072305A (en) * 1990-03-08 1991-12-10 Yamatoya & Co., Ltd. Picture producing apparatus using picture information values correlated to light intensities in tonal conversion formula
US5134494A (en) * 1991-02-04 1992-07-28 Yamatoya & Co., Ltd. Method for producing color and black plates in a multi-color plate making apparatus

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US4833546A (en) * 1987-03-11 1989-05-23 Yamatoya & Co., Ltd. Photomechanical apparatus
US4924323A (en) * 1988-05-13 1990-05-08 Yamatoya & Co., Ltd. Tonal conversion method for pictures
US4956718A (en) * 1988-08-23 1990-09-11 Yamatoya & Co., Ltd. Tonal conversion method for pictures
US5057931A (en) * 1989-08-19 1991-10-15 Yamatoya & Co., Ltd. Tonal conversion method of pictures for producing reproduced pictures free of color-fog
US5072305A (en) * 1990-03-08 1991-12-10 Yamatoya & Co., Ltd. Picture producing apparatus using picture information values correlated to light intensities in tonal conversion formula
US5134494A (en) * 1991-02-04 1992-07-28 Yamatoya & Co., Ltd. Method for producing color and black plates in a multi-color plate making apparatus

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6433898B1 (en) * 1995-08-26 2002-08-13 Heidelberger Druckmaschinen Aktiengesellschaft Method and apparatus for the conversion of color values
US5913014A (en) * 1997-07-21 1999-06-15 Eastman Kodak Company Transforms for digital images
US6842266B1 (en) * 2000-02-25 2005-01-11 Xerox Corporation Systems and methods that determine an image processing system tone reproduction curve
US20060034323A1 (en) * 2004-08-11 2006-02-16 Lars Karlsson Method and technique for the processing and intelligent display of wideband direction-finding data
US20070287395A1 (en) * 2004-08-11 2007-12-13 Lars Karlsson Method and signal intelligence collection system that reduces output data overflow in real-time
US7724680B2 (en) * 2004-08-11 2010-05-25 Agilent Technologies, Inc. Method and technique for the processing and intelligent display of wideband direction-finding data

Also Published As

Publication number Publication date
GB9011672D0 (en) 1990-07-11
DE4011068C2 (de) 2000-03-16
GB2234410B (en) 1993-12-08
GB2234410A (en) 1991-01-30
JP2939270B2 (ja) 1999-08-25
JPH033477A (ja) 1991-01-09
DE4011068A1 (de) 1990-12-06
FR2647994B1 (fr) 1994-02-25
FR2647994A1 (fr) 1990-12-07

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